In the manufacture of glass bottles for example, glass gobs, namely, lumps of molten glass at a temperature within a range from 1100° C. to 1200° C. produced by a feeder mechanism, are introduced into a mold to form a predetermined bottle shape. When a glass bottle is formed from the glass gob, a hollow glass body (a parison) having a bottle opening is formed from the glass gob in a blank mold. A glass bottle as a final product is then produced from the parison in a finishing mold. Conventionally used in a blank molding step are two methods, namely, a blow method for blowing compressed air, and a press method for inserting a plunger. The finishing step typically uses only a blow method for expanding the parison by compressed air.
The quality control of the glass gob is extremely important in the production technique of the glass product. The shape and volume (weight) of the glass gob, in particular, greatly affect the quality, capacity and thickness of the glass product. If the shape and weight of the glass gob is not managed nor controlled with a repeatability, the thickness of the glass product is not stabilized. This means that variations in the quality of the glass products become large, possibly causing wrinkles as well as chill marks or checks (cracks on the surface) on the external surface of the glass product.
In a known technique, the weight of the glass product is manually measured by using an electronic balance, or it is measured by referencing the pressing depth of a machine plunger in a blank molding step in the press method. The measurement results are then fed back in the formation process of the glass gob. The quality control based on the manual process not only requires a complex procedure, but also leads to variations in the measurement from person to person. Quality control cannot be performed with precision. No information concerning the shape of the glass gob is available even if the finished glass product is carefully examined. If any faulty state of an operational factor resulting in a quality defect is detected, a faulty product has already been yielded. In any case, the quality of the glass gob must be recovered by suspending the production of the glass product so that the productivity and yield of the glass products are adversely affected.
A variety of proposals have been made as a method to control the quality of the volume (weight) and the shape of the glass gob, but each of those proposals has the following drawbacks.
(1) A method of monitoring the shape of the glass gob by a single CCD camera or the like may be proposed. With the single camera, only a side of the glass gob is observed to form a two-dimensional image. It is not easy to know the entire configuration and the volume (weight) of the glass gob.
(2) Another method may be proposed in which a glass gob formed by a feeder mechanism is placed on a measurement tray, a plurality of CCD cameras or the like are used to observe the glass gob on the tray, and the volume and the configuration of the glass gob are observed by a three-dimensional image processing technique. However, the shape of a portion of the glass gob in contact with the measurement tray is not observed. The glass gob is deformed and loses the original shape thereof as the molten glass cools with time. Further, the glass gob is possibly deformed in shape with its weight on the measurement tray. The true configuration of the glass gob cannot be known.
(3) A further method may be proposed in which a glass gob after pushed out through an orifice of the feeder mechanism, still suspended to the feeder immediately prior to a cutting operation by shear blades or in the middle of the cutting operation, is observed by a plurality of CCD cameras or the like, and the volume and the configuration of the glass gob are observed by a three-dimensional image processing technique. However, the configuration of the glass gob prior to being cut is different from the configuration of the actually cut glass gob. The weight and the shape of the glass gob as desired cannot be measured with precision. A faulty state of an operational factor functioning as a cause for a quality defect cannot be detected. If an adjustment error, for example, occurs in a drop guide that is provided for guiding the glass gob so as not to be tilted at the cutting operation, the glass gob falling subsequent to the cutting operation takes an inclined posture and may not be received by a scoop funnel in the right position thereof. Even if the glass gob is observed prior to the cutting operation, any faulty operational factors cannot be detected. If a poor cutting operation occurs because of wear of the shear blades or an insufficiently cooled shear blades, the cut surface of the glass gob is deformed, and the quality of the glass product formed in the next step is adversely affected. Such faults included in the shear blades cannot be detected even if the glass gob is observed prior to the cutting operation.